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TT: Tiefe Temperaturen

TT 7: Heavy Fermions

TT 7.6: Hauptvortrag

Dienstag, 23. März 1999, 11:00–11:30, F1

Neutron scattering studies above and below Tc in the heavy fermion superconductor UPd2Al3 — •N. Bernhoeft — Institut Laue Langevin F-38042 Grenoble France

The heavy fermion superconductor UPd2Al3 exhibits the relatively uncommon combination of an antiferromagnetic phase transition, at TN = 14.3 K, followed by a superconducting phase transition below 2 K without destruction of the ordered magnetic moment [1]. Polarised neutron inelastic scattering in the vicinity of the antiferromagnetic ordering wave vector has been used to probe the magnetic fluctuation spectrum in the temperature range 150 mK < T < 20 K. Below TN the response, which is found to be transverse to the sub-lattice moment, exhibits both a spin wave pole [2] and a quasielastic peak centred at the AF propagation vector [3], the latter having a correlation length that increases on lowering the temperature. Below Tc the low energy fluctuations remain transverse and develop an energy gap of 0.35 meV. Independent work corroborates the existence of an energy gap in the neutron spectrum [4]. We show that it is reasonable to consider the superconducting state as arising out of interactions between quasiparticles which are strongly renormalised by the low frequency exchange field.

[1] H Kita et al J Phys Soc Japan 63 726 (1994);

[2] T Petersen et al Physica B199 151 (1994);

[3] N Sato et al J Phys Soc Japan 66 1884 (1997);

[4] N Metoki et al J Phys Soc Japan 66 2560 (1997;